Many laser applications require the laser's frequency to be changed in time (“frequency modulated”) in an extremely controlled and predictable manner over large optical frequency bandwidths. Many of these applications require the optical frequency to change linearly and monotonically in time (to form a “linear frequency chirp,” called simply a “chirp” hereinafter). For instance, researchers have actively linearized an optical frequency radio frequency (RF) sideband to improve the performance of frequency-modulated, continuous-wave (FM-CW) laser detection and ranging (LADAR). Other researchers have actively linearized the carrier optical frequency for reading out spectral information recorded in optical crystal transitions.
Previous work has demonstrated techniques for providing feedback through circuits that drive a laser to provide stable, highly linear laser output for low optical bandwidth systems. This previous work exhibits frequency tuning, including highly linear chirps, with bandwidths of up to 10 gigaHertz (GHz, 1 GHz=109 cycles per second, also called Hertz and abbreviated Hz).